This invention relates to aerodynamic airfoil blades typically utilized in rotating turbomachine, and relates more particularly to improved structure and method for internal cooling of such blades.
Turbomachinery such as a gas turbine engine typically includes a rotary compressor which delivers a high volume flow of pressurized gas flow to a combustion chamber wherein the temperature of the gas flow is increased dramatically. The hot gas flow then passes in momentum exchange relationship with one or more turbine wheels to rotate the turbines and produce useful power. Typically, sets of non-rotating stator vanes are included between serially arranged axial turbine wheels to redirect the gas flow into an appropriate direction for efficient momentum exchange relationship with the next succeeding set of turbine blades. It is well known in such turbomachinery that efficiency increases with increase in temperature of the gas flow. A limiting factor in the gas flow temperature is the high temperature capability of the various turbine and stator blades.
Various arrangements for internally cooling the separate stator and turbine blades have been proposed to increase the upper operating temperature capability of the turbomachinery. Exemplary of prior art structure are the disclosure of various turbomachinery blading illustrated in U.S. Pat. Nos. 3,301,526; 3,515,199; 3,628,880; 3,656,863; and 3,927,952. None of the above referenced patents disclose structure and associated advantages as contemplated by the present invention. For instance, a common technique utilized in prior art laminated blade construction such as depicted in the above referenced U.S. Pat. No. 3,656,863 is the attempt to accomplish transpiration cooling of a turbine or stator blade. Transpiration cooling refers to the technique of exhausting cooling flow through the surface to be cooled substantially perpendicularly into the hot gas flow of the turbomachinery to force the hot gas away from the surface. For better effect it is known to introduce the cooling flow from a plurality of minute passages to promote such transpiration cooling. In contrast to such prior art arrangements however, one purpose of the present invention is to avoid such transpiration cooling techniques and instead utilize more efficient film or convection cooling techniques which minimize interference of the cooling fluid flow with the hot gas stream of the turbomachine in order to minimize efficiency reduction in the turbomachinery.